To know if the installed Ubuntu is of 32 or 64 bits:
uname -m
If it shows i686 or i386 it means 32 bits.
If it shows x86_64 it means 64 bits.

If the CPU is of 32 bits Ubuntu must be of 32 bits.
If the CPU is of 64 bits it can work in 64 or 32 bits. So we can choose: Ubuntu can be of 32 bits or of 64 bits.

To know if the CPU is of 32 or 64 bits:
a) grep -w lm /proc/cpuinfo
If we see lm in red is of 64 bits. Otherwise is of 32 bits.
b) sudo lshw | grep “description: CPU” -A 12 | grep width
It says clearly what we want to know.